Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.84   4.274%   $64.483   $64.48   $64.50   $64.50  
  Purchase #2 $83.93   9.488%   $91.8933   $91.89   $91.90   $91.90  
  Purchase #3 $169.32   4.406%   $176.7802   $176.78   $176.80   $176.80  
  Purchase #4 $80.72   4.718%   $84.5284   $84.53   $84.55   $84.50  
  Purchase #5 $212.85   10.542%   $235.2886   $235.29   $235.30   $235.30  
  Purchase #6 $17.70   9.857%   $19.4447   $19.44   $19.45   $19.40  
  Purchase #7 $87.89   6.764%   $93.8349   $93.83   $93.85   $93.80  
  7 purchase totals = $714.25       $766.2531   $766.24   $766.35   $766.20